A Thai court has issued an arrest warrant for an unnamed suspect in a riverside blast that occurred a day after the bombing of a shrine in central Bangkok that killed 20 people.

Police spokesman Prawut Thawornsiri said the suspect appeared in a security video that shows a blurry image of an unidentified man in a blue shirt kicking a bag into the water near a busy pier on the night of August 17, soon after the explosion at the Erawan Shrine.

An explosion took place near the spot around 18 hours later on August 18, but caused nobody was injured.

The warrant issued by the South Bangkok Criminal Court says the suspect faces three charges including attempted premeditated murder, exploding a bomb that could cause harm and unauthorised possession of explosives, Prawut said. It does not specify the suspect's name or nationality.

Police have not definitively linked the two blasts according to public statements. An arrest warrant was issued last week for a suspect in the deadly explosion at the shrine, also without a name or nationality. No arrests have been made in either case.